# C++ > Algorithms Code Examples

## Binary Search Tree Program

``` Binary Search Tree Program #include <iostream> #include <cstdlib> using namespace std; class BinarySearchTree { private: struct tree_node { tree_node* left; tree_node* right; int data; }; tree_node* root; public: BinarySearchTree() { root = NULL; } bool isEmpty() const { return root==NULL; } void print_inorder(); void inorder(tree_node*); void print_preorder(); void preorder(tree_node*); void print_postorder(); void postorder(tree_node*); void insert(int); void remove(int); }; // Smaller elements go left // larger elements go right void BinarySearchTree::insert(int d) { tree_node* t = new tree_node; tree_node* parent; t->data = d; t->left = NULL; t->right = NULL; parent = NULL; // is this a new tree? if(isEmpty()) root = t; else { //Note: ALL insertions are as leaf nodes tree_node* curr; curr = root; // Find the Node's parent while(curr) { parent = curr; if(t->data > curr->data) curr = curr->right; else curr = curr->left; } if(t->data < parent->data) parent->left = t; else parent->right = t; } } void BinarySearchTree::remove(int d) { //Locate the element bool found = false; if(isEmpty()) { cout<<" This Tree is empty! "<<endl; return; } tree_node* curr; tree_node* parent; curr = root; while(curr != NULL) { if(curr->data == d) { found = true; break; } else { parent = curr; if(d>curr->data) curr = curr->right; else curr = curr->left; } } if(!found) { cout<<" Data not found! "<<endl; return; } // 3 cases : // 1. We're removing a leaf node // 2. We're removing a node with a single child // 3. we're removing a node with 2 children // Node with single child if((curr->left == NULL && curr->right != NULL)|| (curr->left != NULL && curr->right == NULL)) { if(curr->left == NULL && curr->right != NULL) { if(parent->left == curr) { parent->left = curr->right; delete curr; } else { parent->right = curr->right; delete curr; } } else // left child present, no right child { if(parent->left == curr) { parent->left = curr->left; delete curr; } else { parent->right = curr->left; delete curr; } } return; } //We're looking at a leaf node if( curr->left == NULL && curr->right == NULL) { if(parent->left == curr) parent->left = NULL; else parent->right = NULL; delete curr; return; } //Node with 2 children // replace node with smallest value in right subtree if (curr->left != NULL && curr->right != NULL) { tree_node* chkr; chkr = curr->right; if((chkr->left == NULL) && (chkr->right == NULL)) { curr = chkr; delete chkr; curr->right = NULL; } else // right child has children { //if the node's right child has a left child // Move all the way down left to locate smallest element if((curr->right)->left != NULL) { tree_node* lcurr; tree_node* lcurrp; lcurrp = curr->right; lcurr = (curr->right)->left; while(lcurr->left != NULL) { lcurrp = lcurr; lcurr = lcurr->left; } curr->data = lcurr->data; delete lcurr; lcurrp->left = NULL; } else { tree_node* tmp; tmp = curr->right; curr->data = tmp->data; curr->right = tmp->right; delete tmp; } } return; } } void BinarySearchTree::print_inorder() { inorder(root); } void BinarySearchTree::inorder(tree_node* p) { if(p != NULL) { if(p->left) inorder(p->left); cout<<" "<<p->data<<" "; if(p->right) inorder(p->right); } else return; } void BinarySearchTree::print_preorder() { preorder(root); } void BinarySearchTree::preorder(tree_node* p) { if(p != NULL) { cout<<" "<<p->data<<" "; if(p->left) preorder(p->left); if(p->right) preorder(p->right); } else return; } void BinarySearchTree::print_postorder() { postorder(root); } void BinarySearchTree::postorder(tree_node* p) { if(p != NULL) { if(p->left) postorder(p->left); if(p->right) postorder(p->right); cout<<" "<<p->data<<" "; } else return; } int main() { BinarySearchTree b; int ch,tmp,tmp1; while(1) { cout<<endl<<endl; cout<<" Binary Search Tree Operations "<<endl; cout<<" ----------------------------- "<<endl; cout<<" 1. Insertion/Creation "<<endl; cout<<" 2. In-Order Traversal "<<endl; cout<<" 3. Pre-Order Traversal "<<endl; cout<<" 4. Post-Order Traversal "<<endl; cout<<" 5. Removal "<<endl; cout<<" 6. Exit "<<endl; cout<<" Enter your choice : "; cin>>ch; switch(ch) { case 1 : cout<<" Enter Number to be inserted : "; cin>>tmp; b.insert(tmp); break; case 2 : cout<<endl; cout<<" In-Order Traversal "<<endl; cout<<" -------------------"<<endl; b.print_inorder(); break; case 3 : cout<<endl; cout<<" Pre-Order Traversal "<<endl; cout<<" -------------------"<<endl; b.print_preorder(); break; case 4 : cout<<endl; cout<<" Post-Order Traversal "<<endl; cout<<" --------------------"<<endl; b.print_postorder(); break; case 5 : cout<<" Enter data to be deleted : "; cin>>tmp1; b.remove(tmp1); break; case 6 : system("pause"); return 0; break; } } } ```